In a computer system, the processor, the memory, and the input/output (I/O) devices communicate with one another by way of a bus. A bus is a series of conductors, each of which is capable of transmitting signals which represent either data to be transferred between devices on the bus or control information, such as device addresses, which determine when and to where the data being transferred by the bus is to be transferred. The signals transferred on the bus typically take the form of rapidly changing bi-stable voltage levels. These voltage levels are placed on the conductors by bus drivers incorporated into each device which communicates with the bus. For optimum signal power transfer between devices and minimum signal reflection, the bus must be terminated in such a way that the impedance of the bus matches the impedance of the bus drivers. The bus impedance should be held approximately constant.
Generally, bus terminators take the form of modular devices. The bus terminator is physically inserted onto the bus to provide termination and physically removed from the bus to remove termination, for example, when the bus is to be extended. Such changing of the bus termination requires physical access to the bus, which in turn requires the opening of the enclosures protecting the devices and bus.
The present invention permits a bus terminator to be connected to and disconnected from a bus electrically and without being physically moved.
Another feature of the invention is that when the terminator is disconnected from the bus, its internal power supply is reduced substantially.